1. Field of the Invention
The present invention relates to a lens assembly, lens moving device and assembling method. More particularly, the present invention relates to a lens assembly, lens moving device and assembling method, in which moving mechanisms for lenses/lens groups can be suitably arranged in an economized space.
2. Description Related to the Prior Art
A digital still camera is an optical instrument in which an image pickup element such as a CCD photographs an object image. An optical system in a lens assembly of the digital still camera includes movable lenses/lens groups. Information of an in-focus position is derived by evaluating an image signal obtained by the image pickup element. The lenses/lens groups are moved according to the in-focus position to focus the optical system, which is an AF (auto focus) device. U.S.P. Pub. No. 2003/107667 (corresponding to JP-A 2003-149528) discloses the digital still camera having the AF device. The digital still camera has a lens moving mechanism, which includes a lens holder and guide rods. The lens holder holds each one of the lenses/lens groups. The guide rods keep the lens holder movable in an optical axis direction. Also, motors are used in the digital still camera. For the AF operation, one of the motors as prime mover finely moves the lens holder in the optical axis direction by conversion of rotation to linear movement for the lens holder.
A widely available type of the digital still camera has a zooming mechanism with which a magnification is changeable by optical zooming. A plurality of the lens moving mechanisms are incorporated in the digital still camera and arranged in the optical axis direction for zooming. A first one of the lens moving mechanisms disposed on the objective side moves an associated one of the lenses/lens groups, for changing the zooming magnification. A second lens moving mechanism disposed on the focal plane side moves one associated lens/lens group, for adjusting the focus.
However, adjustment of the focusing and zooming by use of a plurality of the lens moving mechanisms enlarges the size of the lens assembly due to difficult arrangement of the motors. A body of the digital still camera should be small in view of a compact construction, but cannot be made small in a sufficient manner for intention. It is conceivable to dispose the motors to direct output shafts of the motors toward one another, so as to cope with the shortcoming. However, wiring for each of the motors is required to connect with a control device in the digital still camera, by use of such a line as a flexible wiring board. A problem arises in a complicated structure and a large size of the flexible wiring board.
The lens assembly includes a housing. A positioning hole is formed for positioning the guide rods. There is a difficulty in known assembly of the lens assembly. Recognition of the positioning hole before inserting the guide rods is not very easy with human eyes, to make it considerably difficult to assemble the lens assembly. Also, the guide rods may strike the inside of the lens housing or edges of the positioning hole during the insertion, to cause scratches or damages on the lens housing due to the use of the guide rods.
An improvement is disclosed in JP-A 8-248283. The lens assembly is provided with an opening, used in the course of assembly of the lens assembly for visually recognizing positions of the guide rods and the positioning hole. Also, an insertion hole for the guide rods is formed with a conical surface in a funnel form, to facilitate the insertion of the guide rods in the lens housing.
However, the assembly of the lens assembly according to JP-A 8-248283 requires observation of the inside of the lens housing through the opening to insert the guide rods in the positioning hole by checking positions of the guide rods and the positioning hole. Accordingly, the operation of the assembly cannot be efficient due to the manual operation, as the assembly of the lens assembly is difficult to automate.
Also, JP-A 10-254022 discloses an aperture stop mechanism, which includes two aperture stop blades, driven electrically to slide in a direction crosswise to the optical axis direction, for adjusting an aperture stop. A shutter opening is formed through a base plate of the aperture stop mechanism. The aperture stop blades are disposed on the base plate in a slidable manner. A drive lever for the aperture stop blades converts rotation of the motors into linear movement, which is transmitted to the aperture stop blades to shift the aperture stop blades in directions opposite to one another. Aperture recesses are formed in the aperture stop blades for defining an aperture at the shutter opening, to vary an aperture stop diameter according to an amount of overlapping of the aperture recesses.
The aperture stop mechanism of JP-A 10-254022 has a simple structure and may be produced at a low cost. The aperture stop mechanism is usable also as a shutter device. With the aperture stop mechanism, it is conceivable to combine path changing optics for changing an optical path with a bend. JP-A 9-033782 discloses an example of the path changing optics. Also, JP-A 2005-084654 discloses lens shift as a basis of the path changing optics, including two lenses/lens groups disposed before and after the shutter device and the aperture stop mechanism, and the guide rods for guiding the lenses/lens groups. However, a problem arises in incorporating the aperture stop mechanism in the path changing optics of the known technique. A space of the aperture stop blades required for moving cannot be obtained sufficiently because the guide rods must extend within a region of movement of the aperture stop blades. If the aperture stop mechanism is disposed to cause the aperture stop blades to move in a direction away from the guide rods, a thickness of the image pickup optical system will be too great. A size of the lens assembly cannot be small sufficiently.